Separation of styrene from ethyl benzene by azeotropic distillation



Patented Nov. 12, 1946 SEPARATION F STYRENE ETHYL BY` AZEOTROPIC DISTILLA- Theodor A. Petry, Wenonah, and Grady LfPayne, Clarksboro, N. J., assignors to Socony-Vacuum Oil Company, Incorporated,l a corporation of New York Application July 1, 1942, serial Nc. 449,358

(c1. ,2oz- 42) Claims. 1 i This invention has to do with the separation of styrene in relatively pure form from crude mixtures containing the same. i

Styrene finds uses in the synthesis of a, number of organic chemicals and polymerization prodl ucts and is of particular interest in connection with certain forms of synthetic rubber. For most of these uses the styrene must be in a relatively \pure state and substantially without polymerized c derivatives present. Crude styrene is normally contaminated with appreciable quantities ormaterials of similar boiling points and fairly closely related chemical' structure such as, for example, ethyl benzene. because of the readily polymerizable nature of styrene, its preparation in a requisite degree -of purity by ordinary distillation methods presents considerable diiliculty. Relatively i complicated and expensive methods are, therefore, frequently employed for obtaining styrene of a high degree of purity. c

This invention has for its principal object the provisionof a method for the recovery of relatively pure styrene from such crude styrene mixtures with a minimum of difficulty and a minimum of degradation of the styrene product itself.

This invention is based upon the discovery that substantially pure styrene can be recovered readilyfrom crude styrene by simple distillation methods conducted in the presence of a properly selected distillation assistant. Such a distillation assistant should be capable of forming constant boilingmixtures with styrene which are considerably higher boiling than those formed with the usual contaminants present in crude styrene. In general, among those distillation assistants which may be used, it is preferable to use those lmembers which permit of a similar separation by water. In general, any polar compound boiling within the range of 90 to 250 C., and preferably one which is water soluble, can be used to eiect the separation. We have found that ethyl Celv losolve, (glycol mono-ethyl ether) is particulary useful in this connection, is soluble in water and can be separated readily from the various products of distillation. The amount of the distillation assistant which will be added depends upon the amount of contaminant present in the charge mixture and upon thenature vcf the distillatign assistant used. Usually the quantity of assistant required varies between 25% and 25,0% by volume of the contaminants in the crude styrene. l

The process for theseparation is shown by the Upon this account and also singlediagrammatic iigure of the drawing attached hereto. y

The effect of the presence of ethyl Cellosolve as a distillation assistant may be indicated by the following operations conducted in batch at atmospheric pressure. In each case the charge mixture consistedof a mixture of 60% by weight of ethyl benzene and 40% by weightrof styrene.

In each case the distillations were conducted in batch at atmospheric pressure employing a fractionating column of about eleven theoretical plates. #In the first case in the absence of the dis- -tillation assistant, the recovery oi condensed product commenced at a tower top temperature of 272 F. and the ,distillation was conducted until 50% of the still charge had been recovered as an overhead product, at which time the tower top In a second operation, the same mixture .of`

ethyl benzene and styrene was used, and the same still was used except that the still charge consisted of one part of the crude styrene mixture and one part vof ethyl Cellosolve. In this case, distillation commenced at a tower top temperature of 250 F. and a' total overhead of 79% by volume of the crude styrene charge (after separation of distillation assistant) was recovered. Of the overhead distillate, 40% was quite pure ethyl benzene and the last 19% taken overhead was unpolymerized styrene of purity. The

intermediate 20% of overhead product was a mixture of styrene and ethyl benzene in which the styrene wasl unpolymerized, which could be subjected tc a second distillation with similar recoveries. The bottoms from this operation when separated from distillation assistant were found to be polymerizedf In these two experiments, which differed only in the presence of ethyl Cellosolve in proper amount as a distillation assistant, it was found that the presence of this distillation assistant enabled the recovery of hal! of the styrene present' in a pure state and of a further portion of the styrene present in an unpolymeri'zed state still capable of recovery by "tion from the distillation products.

could be made.

These operations do not, however, set forth Ithe preferred form of our process for the recovery of styrene of high purity from such mixtures. The polymerization of styrene is a matterof time and temperature. We havefound 'that by conducting a distillation at relatively reduced pressure and in the presense of a distillation assistant, distillation operations may be conducted for the recovery of styrene in a high state of purity without the loss of any styrene by polymerization.

` For example, using the same crude styrene mixture containing 40% by weight of styrene and 60% by weight of ethyl benzene, adding an equal volume of ethyl Cellosolve, and distilling in a batch distillation, at a pressure of 55 mm. of

mercury at the top oi the fractionating column,

using a fractionating column containing the equivalent of 2'? theoretical fractionating plates, it was found that the ilrst 51% taken overhead was substantially pure ethyl benzene having a refractive index oi 1.492 (Num.) compared to a refractive index of 1.4958 for reagent grade ethyl benzene, that the next25% taken overhead in styrene present was directly recovered in a high state of purity, the remainder being contained in a mixturenot unlike the original charge. Additionally, the method-of operation was an ex` ceedinglyl simple one involving the use only of materials capable of ready and eiective separa- It did not involve the introduction into the distillation products of anything of the nature of an lnor interfere with the further use of the styrene product.

In its most eifective form, this process may be conducted as a continuous operation in a column of high Iractionating eilciency from which relatively pure styrene containing some of the distilmarily ethyl benzene, which consists of subjecthibitor which might later require costly removal ing a mixture containing crude styrene to distillation in the presence of glycol monoethyl ether as a distillation assistant, recovering from said distillation at least two fractions, one consisting 'of "substantially pure styrene and some of the distillation assistant and the other consisting oi a mixture of contaminants and distillation as sistant and separating the distillation assistant from the styrene containing fraction.

2. That method o! `recovering relatively purev styrene from crude mixtures comprising styrene and contaminants of similar boiling point, primarily ethyl benzene, which consists of subjecting a mixture containing crude styrene to distillation in the presence'of glycol mono-ethyl ether to the extent of not less than 25% by volume of the crude styrene mixture, recovering from said distillation at least two fractions, one consisting of substantially pure styrene and some of the distillation assistant and the other consisting of a mixture of contaminants and distillation assistant and separating the distillation assistant from the styrene containing fraction.

3. That method of recovering relatively pure styrene from crude mixtures comprising styrene and contaminants of similar boilingwpoint, primarily ethyl benzene, which consists of subjecting a mixture containing crude styrene to distillation under pressure substantially less than atmospheric in the presence of glycol mono-ethyl ether as a distillation assistant, recovering from said distillation at least two fractions, one consisting of substantially pure styrene and some of the distillation assistant and the other consisting of a mixture of contaminants and distillation assistant from the styrene containing fraction.

' 4. That method of recovering relatively purev styrene from crude mixtures comprising styrene and contaminantsofsimilar boiling point, primarily ethyl benzene, which consists of subjecting a mixture containing crude styrene to distillation under pressure substantially less than atmospheric in the presence of glycol monoethyl ether to the extent of not less than 25% by volume of the crude styrene mixture, recover-A ing from said distillation at least two fractions, one consisting of substantially pure styrene and some of the distillation assistant andthe other consisting of a mixture of contaminants and distillation assistant and separating the distillation y a binary azeotrope primarily of ethyl benzene and the ethylene glycol mono-ethyl ether and recovering the concentrated vstyrene fraction Certicate of Correction p Patent No. 2,411,106. f November 12, 194e.

THEODOR A. PETRY ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 2,v line 18, for has read had; column 3, line 24, for the' numeral 1.492 read 1.4962; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 25th day of February, A. D. 1947.

LESLIE FRAZER,

First Assistant Commissioner of Patents.

Disclaimer 2,411,106.-Theodor A. Petry, Wenonah, and Grady L. Payne, Clarksboro, N. J. SEPARATION 0F STYRENE FROM ETHYL BENZENE BY AzEoTRoPIC DISTILLA- TION. Patent dated Nov. 12, 1946. Disclaimer led July 23, 1948, by the assignee, Socony-Vacuum Oil Company, Incorporated. Hereby enters this disclaimer to claims 1, 2, 3, 4, and 5.

[Oficial Gazette August 17, 1.948.] 

